An unusual and chemoselective reduction of ester grouping in nsubstituted-3-acetylindoles by sodium borohydride

Article abstract of DOI:10.2174/157017812800167402

Treatment of 3-acetylindoles 1(a-e) with ethyl chloroacetate in the presence of K₂CO₃ and tetrabutylammoniumbromide (TBAB) as phase transfer catalyst in DMF, resulted in the formation of the corresponding N-substituted derivatives, e

Full text of DOI:10.2174/157017812800167402

192
Letters in Organic Chemistry, 2012, 9, 192-197
An Unusual and Chemoselective Reduction of Ester Grouping in N-
substituted-3-acetylindoles by Sodium Borohydride
Muvvala Venkatanarayana* and Pramod K. Dubey
Department of Chemistry, Jawaharlal Nehru Technological University, Hyderabad College of Engineering, Kukatpally,
Hyderabad (A.P), 500 085, India
Received March 17, 2011: Revised October 27, 2011: Accepted December 07, 2011
Abstract: Treatment of 3-acetylindoles 1(a-e) with ethyl chloroacetate in the presence of K2CO3 and
tetrabutylammoniumbromide (TBAB) as phase transfer catalyst in DMF, resulted in the formation of the corresponding
N-substituted derivatives, ethyl 2-(3-acetyl-1H-indol-1-yl)acetate 2(a-e) which on reaction with NaBH4 yielded,
unexpectedly, ethanol derivatives, 1-(1-(2-hydroxyethyl)-1H-indol-3-yl)ethanone 3(a-e) by the unusual and
chemoselective reduction of ester grouping in preference to the acetyl group. Alternative synthesis of the latter was
achieved by the treatment of 1(a-e) with 2-chloroethanol under phase transfer catalytic conditions (PTC). 1(a-e), on
treatment with benzenesulphonyl chloride, under PTC conditions, yielded the corresponding N-benzenesulphonyl-3-
acetylindoles 7(a-e), which on reduction with NaBH4 in methanol afforded the corresponding hydroxy derivatives N-
benzenesulphonyl-(ꢀ-hydroxyethyl)indoles 8(a-e). These reactions throw light on the ease of reduction of the 3-acetyl
group on indoles with NaBH4.
Keywords: 3-acetylindole, N-benzenesulphonyl-3-acetylindole, chemoselective, reduction, NaBH4-MeOH.
INTRODUCTION
yl)acetates and 1-benzenesulphonyl-3-acetylindoles giving
the alcohols using NaBH4-MeOH system.
Reduction plays a very important role in organic
synthesis. One of the most common reagents used for this
purpose is sodium borohydride [1]. Usually, the reactions
carried out with NaBH4 are safe, inexpensive and can be
done under mild conditions [2, 3]. Although this reducing
agent has been constantly used for reduction of aldehydes,
ketones and other important functional groups, it is not
commonly used for the reduction of esters [4-7].
RESULTS AND DISCUSSION
Treatment of each of the 3-acetylindoles 1(a-e)
independently, with ethyl chloroacetate in the presence of a
mild base i.e. K2CO3, tetrabutylammoniumbromide (TBAB)
as a phase transfer catalyst, in DMF at r.t. for 1 h, resulted in
the formation of ethyl 2-(3-acetyl-1H-indol-1-yl)acetate
products 2(a-e) respectively in 89-95% yields which when
treated with NaBH4 in methanol at r.t. within 5 min afforded
unexpectedly, ethanol derivatives i.e. 1-(1-(2-hydroxyethyl)-
1H-indol-3-yl)ethanone of 3 (a-e) respectively in 79-85%
yields instead of the expected 4 (a-e) or 5(a-e) (Scheme 1)
(Table 1).
Due to this low reactivity towards esters, the use of
additives to enhance the activity of NaBH4 has been reported
[8]. For example, the addition of iodine to NaBH4 in THF
provides H3B–THF, which is useful for hydroborations,
reduction of esters and various other functional groups [9].
Another example is the addition of zinc chloride along with
the presence of tertiary amine that enhances the reducing
property of NaBH4 toward ester function [8].
Alternative synthesis of 3(a-e) was achieved by the
treatment of 1(a-e) with 2-chloroethanol in the presence of
K2CO3 and TBAB in DMF at r.t. for 1 h, yielding the
products in almost equal yields as above. 3a on treatment
with NaBH4 in methanol at r.t. or even under refluxing for 24
h gave, almost quantitatively 3a on processing the reaction
mixture instead of the expected 4a or 5a.
3-Acetylindole derivatives [11] have been the centre of
attention of researchers over many years due to the high
practical value of these compounds [12], the unusually broad
spectrum of biological activities occupying the first place
[13]. For example, 4- (1H-indol-3-yl)-2-hydroxy-4-oxobut-
2-enoic acid was useful as an anti-HIV agent [14]. Other
compounds derived from 3-acetylindoles are used in the
treatment of gastrointestinal, cardiovascular and CNS
disorders, and also used as HIV-1 integrate inhibitors [10].
Each of the compounds, 1(a-e) when treated with NaBH4
in methanol at r.t. or even under refluxing conditions for 24
h, gave the starting 1(a-e) almost quantitatively, on
processing the reaction mixture, instead of the expected 6(a-
e). 1(a-e), when treated independently with benzenesul-
phonyl chloride in the presence of K2CO3 and TBAB in
CHCl3 at r.t. for 1 h, gave 7(a-e) in 90-98% yields, each of
which on independent reduction with NaBH4 in methanol at
r.t. for just 3 min led to the formation of the corresponding
alcohols 8(a-e) (Scheme 1) (Table 2).
In this context, the aim of the present article is to
describe the reduction of ethyl 2-(3-acetyl-1H-indol-1-
*Address correspondence to this author at the Department of Chemistry,
Jawaharlal Nehru Technological University, Hyderabad College of
Engineering, Kukatpally, Hyderabad (A.P), 500 085, India; Tel: 040-2315-
8661, Ext: 4331; Fax: 040-2305-7787; E-mail: venkatmuvvala@in.com
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

An Unusual and Chemoselective Reduction of Ester Grouping
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
193
O
HO
CH3
CH3
R
NaBH4 / MeOH / RT/ 2-3 min
R
N
R1
N
R1
O
S
O
O
S
O
7(a-e)
HO
SO2Cl
8(a-e)
R
CH3
/ K2CO3 / CHCl3 / TBAB / RT / 1 h
ꢀ
R1
N
CHCOOEt
O
4(a-e)
O
Cl-CH2COOC2H5 / K2CO3
R
CH3
NaBH4 / MeOH /
RT 5 min
R
CH3
O
R1
N
DMF / TBAB / RT/ 1 h
R
CH3
R1
N
CH2COOC2H5
H
2(a-e)
R1
N
1(a-e)
CH2CH2OH
Cl-CH2CH2-OH / K2CO3 / TBAB / DMF / RT / 1 h
3(a-e)
NaBH4 / MeOH / RT / 24 h
ꢀ
NaBH4 / MeOH / RT / 24 h
ꢀ
HO
R
CH3
R1
N
H
HO
R
CH3
NaBH4 / MeOH / RT
6(a-e)
ꢀ
R1
N
CH2CH2OH
5(a-e)
Scheme 1. Reduction of ester grouping on N-substitued-3-acetylindoles by using NaBH4.
Table 1. Preparation of N-ethylacetate-3-acetylindoles and their Corresponding Alcohols*,#
S. No.
Starting material used
Reaction conditions
Product obtained
Yield (%)
M.P (OC)
1.
2
1a(R=H, R1=H)
1b(R=OMe, R1=H)
1c(R=H, R1=OMe)
1d(R=Br, R1=H)
1e(R=NO2, R1=H)
2a(R=H, R1=H)
RT / 1 h
RT / 1 h
2a(R=H, R1=H)
2b(R=OMe, R1=H)
2c(R=H, R1=OMe)
2d(R=Br, R1=H)
2e(R=NO2, R1=H)
3a(R=H, R1=H)
91
89
85
92
95
84
79
82
85
83
120
115-117
178-180
126
3.
4.
5.
6.
7.
8.
9.
10
RT / 1 h
RT / 1 h
RT / 1 h
RT/ 5 min
RT / 5 min
RT / 5 min
RT / 5 min
RT / 5 min
168-170
122
2b(R=OMe, R1=H)
2c(R=H, R1=OMe)
2d(R=Br, R1=H)
2e(R=NO2, R1=H)
3b(R=OMe, R1=H)
3c(R=H, R1=OMe)
3d(R=Br, R1=H)
3e(R=NO2, R1=H)
90
156-157
112
* = Reaction Conditions: 3-acetylindoles, ethyl chloroacetate, TBAB, K2CO3 / DMF / RT / 1 h.
# = Reaction Conditions: N-ethylacetae-3acetylindoles, NaBH4 / MeOH / RT / 5 min.
In the above reactions, for example in the conversion of
2ꢀ3, only the ester group gets reduced with NaBH4 instead
of the keto carbonyl. This is probably due to the fact that the
keto carbonyl group exists predominantly in the form of
enolate ion due to conjugation between the double bond and
lone pair electrons of indole nitrogen (Sheme 2). In ester

194 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
Venkatanarayana and Dubey
Table 2. Preparation of 1-benzenesulphonyl-3-acetylindole and their Corresponding Alcohols*,#
S. No.
Starting Material
Reaction Conditions
Product obtained
Yield (%)
M.P (OC)
1.
2
1a(R=H, R1=H)
1b(R=OMe, R1=H)
1c(R=H, R1=OMe)
1d(R=Br, R1=H)
1e(R=NO2, R1=H)
7a(R=H, R1=H)
RT / 1 h
RT / 1 h
7a(R=H, R1=H)
7b(R=OMe, R1=H)
7c(R=H, R1=OMe)
7d(R=Br, R1=H)
7e(R=NO2, R1=H)
8a(R=H, R1=H)
98
94
92
94
90
88
82
80
81
86
245
>280
199-200
>280
212
45
3.
4.
5.
6.
7.
8.
9.
10
RT / 1 h
RT / 1 h
RT / 1 h
RT/ 2 min
RT / 3 min
RT / 3 min
RT / 3 min
RT / 2 min
7b(R=OMe, R1=H)
7c(R=H, R1=OMe)
7d(R=Br, R1=H)
7e(R=NO2, R1=H)
3b(R=OMe, R1=H)
3c(R=H, R1=OMe)
3d(R=Br, R1=H)
3e(R=NO2, R1=H)
39
61
74
58
* = Reaction Conditions: 3-acetylindoles, benzenesulphonyl chloride, TBAB, K2CO3 / DMF / RT / 1 h.
# = Reaction Conditions: 1-benzenesulphonyl-3-acetylindole, NaBH4 / MeOH / RT / 2-3 min.
NaBH4
ꢀ
´
O
O
O
CH3
CH3
CH3
R
R
R
N
R1
N
R1
N
CH2COOC2H5
R1
CH2COOC2H5
CH2COOC2H5
(2B)
(2A)
(2)
Scheme 2. The plausible resonance structures of N-ethylacetat-3-acetylindole.
carbonyl group, such type of conjugation is absent and it
exists in the keto form only. That is why it reacts with
NaBH4 resulting in reduction. This is shown below with the
help
ethyl 2-(3-acetyl-1H-indol-1-yl)acetates 2(a-e) and the keto
group in 1-benzenesulphonyl-3-acetylindoles 7(a-e) in
methanol at r.t. only. Moreover, ethyl 2-(3-acetyl-1H-indol-
1-yl)acetate 2(a-e) and 1-benzenesuphonyl-3-acetylindole
7(a-e) could be readily prepared by the reaction of 3-
acetylindole with ethyl chloroacetate and benzenesulphonyl
chloride respectively, under mild conditions using PTC
method.
of resonance structures involving 2 and 2A (Scheme 2).
This line of explanation further seems to be supported by the
fact that the parent compounds, i.e. simple 3-acetylindoles
1(a-e), are resistant to the reduction of the keto carbonyl at
3-postion with NaBH4 in methanol either at r.t. or at reflux
even after 24 h. Also, simple N-methyl or N-ethyl-3-
acetylindoles were resistant to reduction with NaBH4 in
methanol even when kept at r.t. for 24 h.
EXPERIMENTAL SECTION
Melting points were determined using a Buchi melting
point B-545 apparatus and were uncorrected. TLC checking
was done on glass plates coated with Silica Gel –G and
spotting was done using iodine or UV lamp. IR spectra were
recorded using Perkin Elmer model-2000 FT-IR instrument
In the case of 7, the reduction of the keto group of 3-
acetyl moiety seems to be facile because, in 7 the
benzenesulphonyl group on indole exerts a strong electron
withdrawing field effect on the nitrogen, preventing the
facile resonance as observed in 2A between the indole-2, 3-
double bond and the acetyl group, thereby allowing an attack
by hydride ion on the electrophilic carbonyl carbon of 7.
1
in KBr phase. H- NMR spectra were recorded on a Bruker
DPX 400- instrument operating at 400 MHz.
General Procedure for the Preparation of 2 from 1
To a stirred solution of DMF containing K2CO3 (4.14
gms, 30 mmol) and catalytic amount of TBAB (0.5 gms) was
added 1 (10 mmol), followed by ethyl chloroacetate (1.3 ml,
12 mmol) and the resulting mixture stirred at r.t. for 1 h. At
CONCLUSION
We have observed in the above reactions that NaBH4
brings about the chemoselective reduction of ester group in

An Unusual and Chemoselective Reduction of Ester Grouping
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
195
the end of this period, the mixture was poured into ice-cold
(100 ml) water. The separated solid was filtered, washed
with water, dried and recrystallized from hot ethyl acetate to
obtain pure 2.
separated solid was filtered, washed with water and dried to
obtain crude 3 which on recrystallization from hot ethyl
acetate gave pure 3.
2a: Colorless solid; m.p. 90 ꢀC ; Yield = 2.22 gms
(91%); IR(KBr): 1742 cm-1 (sharp, strong, -CO, ester
carbonyl) and 1638 cm-1 (sharp, strong, -CO, keto carbonyl);
1H- NMR (DMSO-d6/TMS): ꢁ1.24 (t, J = 7.2 Hz, 3H, -CH3),
2.44 (s, 3H, -CO-CH3), 4.20 (q, J = 7.2 Hz 2H, -CH2), 5.25
(s, 2H, N-CH2), 7.21-8.10 (m, 4H, aryl protons of the indole
ring), 8.4 (s, 1H, ꢂ-proton of the indole ring); MS m/z: 246
(M.+ +1); Elemental Anal. Calcd. for C14H15NO3: C 68.56 %,
H 6.16 %, N 5.71%. Found: C 68.61 %, H 6.19 %; N 5.66
%.
Alternative Method for the Preparation of 3 from 1
To a stirred solution of DMF containing K2CO3 and
catalytic amount of TBAB was added 1 (10 mmol) followed
by chloroethanol (1.4 ml, 20 mmol). The whole mixture was
then stirred at r.t. for 1 hr. At the end of this period, the
solution was poured into ice-cold water. The separated solid
was washed with water, dried and recrystallized from hot
ethyl acetate to obtain pure 3.
ꢀ
3a: Colorless solid; m.p. 168-170 C; Yield = 1.70 gms
(84%); IR(KBr): 3420cm-1 (broad, medium, –OH) and 1616
2b: Colorless solid; m.p. 120 ꢀC; Yield = 2.44 gms
(89%); IR(KBr): 1742 cm-1 (strong, sharp due to ester
carbonyl stretching –O-CO) and 1639 cm-1(sharp, strong due
1
cm-1 (strong, sharp, –CO); H- NMR (DMSO-d6/TMS): ꢁ
2.42 (s, 3H, -CH3), 3.75 (q, 2H, -CH2-OH), 4.29-4.31(t, 2H,
-N-CH2), 4.99 (t, 1H, -OH, D2O-exchangeble proton), 7.16-
7.25 (m, 2H,), 7.55-7.57 (m, 1H), 8.16-8.29 (m, 2H, one is
aryl proton of the indole ring and one is ꢂ-proton of the
indole ring); MS m/z: 204 M.+ +1); Elemental Anal. Calcd.
for C12H13NO2: C 70.92 %, H 6.45 %, N 6.89 %. Found: C
71.01 %, H 6.50 %, and N 6.93 %.
3b: Colorless solid; m.p. 120-121 ꢀC; Yield = 1.84 gms
(79%); IR (KBr): 3360 cm-1 (broad, medium, -OH) and 1623
cm-1 (strong, sharp, -CO); 1H- NMR spectrum (DMSO-
d6/TMS): ꢁ 2.41 (s, 3H, -CO-CH3), 3.63 (s, 3H, -OCH3),
3.78 (t, 2H, -N-CH2), 4.98 (t, 2H, -CH2-OH), 5.02 (t, 1H,
D2O-exchangeble, -OH), 7.32-8.12 (m, 3H), 8.34 (s, 1H, ꢂ-
proton of the indole ring); MS m/z = 234(M+. +1); Elemental
Anal. Calcd. for C13H15NO3: C 66.94 %, H 6.48 %, N 6.00
%. Found: C 67.00 %, H 6.51 %, and N 5.97 %.
1
to carbonyl stretching -CO); H- NMR spectrum (DMSO-
d6/TMS): ꢁ 1.21 (t, J = 7.2 Hz, 3H, -CH3), 2.48 (s, 3H, -CO-
CH3), 3.63 (s, 3H, -O-CH3) 4.16 (q, J = 7.2, 2H, -CH2), 5.14
(s, 2H, -N-CH2), 7.33-8.29 (m, 3H), 8.40 (s, 1H, ꢂ-proton of
the indole ring); MS m/z = 276(M+. +1); Elemental Anal.
Calcd. for C15H17NO4: C, 65.44 %; H, 6.22 %; N, 5.09 %.
Found: C, 65.39 %; H, 6.26 % and N, 5.14 %.
2c: Colorless solid; m.p. 115-117 ꢀC; Yield = 2.33 gms.
(85%); IR (KBr): 1741 cm-1 (strong, sharp, -CO, ester
carbonyl) and 1641 cm-1(sharp, strong, -CO); 1H- NMR
(DMSO-d6/TMS): ꢁ 1.22 (t, J = 7.2 Hz, 3H), 2.50 (s, 3H, -
CO-CH3), 3.65 (s, 3H, -O-CH3) 4.17 (q, J = 7.2, 2H), 5.25
(s, 2H, N-CH2), 7.39-8.32 (m, 3H), 8.39 (s, 1H, ꢂ-proton of
the indole ring); MS m/z = 276(M+. + 1); Elemental Anal.
Calcd. for C15H17NO4: C, 65.44 %; H, 6.22 %, N, 5.09 %.
Found: C, 65.39 %; H, 6.26 %; N, 5.14 %.
2d: Colorless solid; m.p. 178-180 ꢀC; Yield = 3.23 gms
(92%); IR(KBr): 1743 cm-1 (strong, sharp, -CO, ester
carbonyl) and 1636 cm-1(sharp, strong, -CO); 1H- NMR
(DMSO-d6/TMS): ꢁ 1.22 (t, J = 7.2 Hz, 3H), 2.50 (s, 3H, -
CO-CH3), 4.18 (q, J = 7.2, 2H), 5.23 (s, 2H, -N-CH2), 7.20-
8.20 (m, 3H), 8.32 (s, 1H, ꢂ-proton of the indole ring); MS
m/z = 324(M+. +1); Anal. Calcd. for C14H14BrNO3: C 51.87
%, H 4.35 %, N 4.32 %. Found: C 51.96 %, H 4.40 %, and N
4.29 %.
2e Colorless solid; m.p. 126 ꢀC; Yield = 2.75 gms (95%);
IR (KBr): 1735 cm-1 (strong, sharp, -CO, ester carbonyl) and
1656 cm-1(sharp, strong, -CO); 1H- NMR spectrum (DMSO-
d6/TMS): ꢁ 1.24 (t, J = 7.2 Hz, 3H), 2.51 (s, 3H, -CO-CH3),
4.19 (q, J = 7.2, 2H), 5.37 (s, 2H, -N-CH2), 7.79-8.6 (m,
3H), 9.061 (s, 1H, ꢂ-proton of the indole ring); MS m/z =
291(M+. +1); Elemental Anal.Calcd. for C14H14N2O5: C 57.93
%, H 4.86 %, N 9.65 %. Found: C 57.99 %, H 4.84 %, and N
9.70 %.
ꢀ
3c: Colorless solid; m.p. 89-90 C; Yield = 1.91 gms
(82%); IR (KBr): 3360 cm-1 (broad, medium, -OH), 1630
cm-1 (strong, sharp, -CO); 1H- NMR spectrum (DMSO-
d6/TMS): ꢁ 2.43 (s, 3H, -CO-CH3), 3.61 (s, 3H, -OCH3),
3.79 (t, 2H, -N-CH2), 4.98 (t, 2H, -CH2-OH), 5.04 (t, 1H,
D2O-exchangeble, -OH), 7.36-8.19 (m, 3H), 8.29-8.30 (s,
1H, ꢂ -proton of the indole ring); MS m/z = 234(M+. +1);
Elemental Anal. Calcd. for C13H15NO3: C 66.94 %, H 6.48
%, N 6.00 %. Found: C 67.00 %, H 6.51 %, and N 5.97 %.
3d: Colorless solid; m.p. 156-157 ꢀC; Yield = 2.38 gms
(85%); IR (KBr): 3342 cm-1 (broad, medium, -OH ) and
1638 cm-1 (strong, sharp, -CO); 1H- NMR (DMSO-d6/TMS):
ꢁ 2.42 (s, 3H, -CO-CH3), 3.83 (t, 2H, -N-CH2), 4.93 (t, 2H, -
CH2-OH), 5.1 (t, 1H, D2O-exchangeble, -OH), 7.23-8.24 (m,
3H), 8.35 (s, 1H, ꢂ -proton of the indole ring); MS m/z =
282(M+. +1); Elemental Anal. Calcd. for C12H12BrNO2: C
51.09 %, H 4.29 %, N 4.96 %. Found: C 51.11 %, H 4.26 %,
and N 4.90 %.
ꢀ
3e: Colorless solid; m.p. 111-112 C; Yield = 2.48 gms
(83%); IR (KBr): 3349 (broad, medium, -OH), 1646 (strong,
sharp, -CO); H- NMR (DMSO-d6/TMS): ꢁ 2.42 (s, 3H, -
General Procedure for the Preparation of 3 from 2
1
A mixture of 2 (10 mmol) and NaBH4 (0.42 gms, 11
mmol) in methanol was stirred at r.t. for 5 min. Progress of
the reaction was monitored by TLC. After completion of the
reaction (5 min), the mixture was poured into ice-cold water
(40 ml), treated with aq. HCl (2%, 5 ml) until neutral. The
CO-CH3), 3.99 (t, 2H, -N-CH2), 4.96 (t, 2H, -CH2-OH), 5.01
(t, 1H, D2O-exchangeble, -OH), 7.65-8.45 (m, 3H), 9.03 (s,
1H, ꢂ -proton of the indole ring); MS m/z = 249(M+. +1);
Elemental Anal. Calcd. for C12H12N2O4: C 58.06 %, H 4.87
%, N 11.29 %. Found: C 58.03 %, H 4.91 %, and N 11.31 %.

196 Letters in Organic Chemistry, 2012, Vol. 9, No. 3
Venkatanarayana and Dubey
General Procedure for the Preparation of 7 from 1
min. Progress of the reaction was monitored by TLC. After
completion of the reaction (3 min), the mixture was poured
into ice-cold water (40 ml), treated with aq. HCl (2%, 5 ml)
until neutral. The separated solid was filtered, washed with
water and dried to obtain crude 8 which on recrystallization
from hot ethyl acetate gave pure 8.
8a: Colorless solid; m.p. 45 ꢀC; Yield = 2.64 gms (88%);
IR(KBr):3390 cm-1 (medium, broad, –OH), 1176 and
1124cm-1 ( strong, –SO2); H1- NMR (DMSO-d6/TMS): ꢁ
1.43 (d, J = 6.8, 3H, -CH3), 4.94 (q, J = 5.6, 1H, -CH),
5.23(d, J = 4.8, 1H, -OH, D2O-exchangeble), 7.21-7.96 (m,
10H, five phenyl protons + four aryl protons + one is ꢂ -
proton of the indole ring); MS m/z: 300 (M.+ -1); Elemental
Anal. Calcd. for C16H15NO3S: C 63.77 %, H 5.02 %, N 4.65
%. Found: C 63.79 %, H 5.09 %, and N 4.68 %.
8b: Colorless solid; m.p. 36 ꢀC; Yield = 2.71 gms (82%);
IR(KBr): 3384 cm-1 (medium, broad, –OH), 1169 and
1131cm-1 ( strong, –SO2); H1- NMR (DMSO-d6/TMS): ꢁ
1.43 (d, J = 6.81, 3H, -CH3), 3.62 (s, 3H, -OCH30, 4.90 (q, J
= 5.6, 1H, -CH), 5.22 (d, J = 4.8, 1H, -OH, D2O-
exchangeble), 7.21-8.31 (m, 9H, five phenyl protons + three
aryl protons + one is ꢂ -proton of the indole ring); MS m/z:
333 (M.+ +1); Elemental Anal Calcd. for C17H17NO4S: C
61.61 %, H 5.17 %, N 4.23 %. Found: C 61.70 %, H 5.10 %,
and N 4.20 %.
8c: Colorless solid; m.p. 61 ꢀC; Yield = 2.64 gms (80%);
IR(KBr): 3400 cm-1 (medium, broad, –OH), 1171 and
1129cm-1 ( strong, –SO2); H1- NMR (DMSO-d6/TMS): ꢁ
1.41 (d, J = 6.8, 3H, -CH3), 3.59 (s, 3H, -OCH3), 4.93 (q, J =
5.6, 1H, -CH), 5.21 (d, J = 4.8, 1H, -OH, D2O-exchangeble),
7.24-8.21 (m, 9H, five phenyl protons + three aryl protons +
one is ꢂ -proton of the indole ring); MS m/z: 333 (M.+ +1);
Elemental Anal. Calcd. for C17H17NO4S: C 61.61 %, H 5.17
%, N 4.23 %. Found: C 61.70 %, H 5.10 %, and N 4.20 %.
8d: Colorless solid; m.p. 74 ꢀC; Yield = 3.06 gms (80%);
IR(KBr): 3381 cm-1 (medium, broad, –OH), 1176 and
1126cm-1 (strong, –SO2); H1- NMR (DMSO-d6/TMS): ꢁ 1.48
(d, J = 6.9, 3H, -CH3), 4.84 (q, J = 5.5, 1H, -CH), 5.29 (d, J
= 4.8 1H, -OH, D2O-exchangeble), 7.29-8.39 (m, 9H, five
phenyl protons + three aryl protons of the indole ring + one
is ꢂ -proton of the indole ring); MS m/z: 380 (M.+ +1);
Elemental Anal Calcd. for C16H14BrNO3S: C 50.54 %, H
3.71 %, N 3.68 %. Found: C 50.60%, H 3.82 %, and N 3.66
%.
8e: Colorless solid; m.p. 58 ꢀC; Yield = 3.46 gms (86%);
IR(KBr): 3406 cm-1 (medium, broad, –OH), 1170 and
1120cm-1 ( strong, –SO2); H1- NMR (DMSO-d6/TMS): ꢁ
1.49 (d, J = 6.9, 3H, -CH3), 4.94 (q, J = 5.6, 1H, -CH), 5.40
(d, J = 4.9, 1H, -OH, D2O-exchangeble), 7.32-8.49 (m, 9H,
five phenyl protons + three aryl protons of the indole ring +
one is ꢂ -proton of the indole ring); MS m/z: 347 (M.+ +1);
Elemental Anal. Calcd. for C16H14N2O5S: C 55.48 %, H 4.07
%, N 8.09 %. Found: C 55.54 %; H 4.02 % and N 8.12 %.
To a stirred solution of CHCl3 containing K2CO3 (4.14
gms, 30 mmol) and catalytic amount of TBAB was added 1
(10 mmol), followed by benzenesulphonoyl chloride (1.42
ml, 11 mmol) and the reaction mixture stirred at r.t. for 1h.
At the end of this period, the reaction mixture was poured
into ice-cold (50 ml) water and the organic layer was
separated. The separated organic layer was evaporated to
obtain the crude solid product 7 which on recrystallization
from hot methanol gave pure 7.
7a: Colorless solid; Yield = 2.93 gms (98%); m.p: > 245
ꢀC; IR(KBr) 1688 cm-1 (sharp, strong, –CO), and a strong
unequal doublet at 1170 and 1140 cm-1 (due to –SO2); H-
1
NMR (DMSO-d6/TMS): ꢁ 2.4(s, 3H, -CH3), 7.31-8.17(m,
9H, five phenyl + four aryl protons of the indole ring), 8.31
(s, 1H, ꢂ -proton of the indole ring); MS m/z: 300 (M+. +1);
Elemental Anal. Calcd. for C16H13NO3S: C 64.20 %, H 4.38
%, N 4.68 %. Found: C 64.18 %, H 4.37 %, and N 4.62 %.
7b: Grey colored solid; Yield = 3.09 games (94%); m.p:
ꢀ
> 280 C; IR(KBr): 1691 cm-1 (sharp, strong, –CO), and a
strong unequal doublet at 1169 and 1114 cm-1 (due to –SO2);
1H- NMR (DMSO-d6/TMS): ꢁ 2.61 (s, 3H, -CH3), 3.76 (s,
3H, -OCH3), 7.36-8.21 (m, 8H, five phenyl + three aryl
protons of the indole ring), 8.63 (s, 1H, ꢂ -proton of the
indole ring); MS m/z: 330 (M+. +1); Elemental Anal. Calcd.
For C17H15NO4S: C 61.99 %, H 4.59 %, and N 4.25 %.
Found: C 62.01 %, H 5.00 % and N 4.21 %.
7c: Colorless solid; Yield = 3.02 gms (92%); m.p: 199-
ꢀ
200 C; IR (KBr): 1696 cm-1 (sharp, strong, –CO), and a
strong unequal doublet at 1170 and 1116 cm-1 (due to –SO2);
1H- NMR (DMSO-d6/TMS): ꢁ 2.62 (s, 3H, -CH3), 3.74 (s,
3H, -OCH3), 7.30-8.19 (m, 8H, five phenyl + three aryl
protons of the indole ring), 8.34 (s, 1H, ꢂ -proton of the
indole ring); MS m/z: 330 (M+. +1); Elemental Anal. Calcd.
for C17H15NO4S: C 61.99 %, H 4.59 %, N 4.25 %. Found: C
62.01 %, H 5.00 %, and N 4.21 %.
7d: Ash Colored solid; Yield = 3.40 gms (94%); m.p. >
ꢀ
280 C; IR (KBr) 1699 cm-1 (sharp, strong, –CO), and a
strong unequal doublet at 1174 and 1117 cm-1 (due to –SO2);
1H- NMR (DMSO-d6/TMS): ꢁ 2.59 (s, 3H, -CH3), 7.28-8.12
(m, 8H, five phenyl an+ three aryl protons of the indole
ring), 8.53 (s, 1H, ꢂ -proton of the indole ring); MS m/z: 378
(M+. +1); Elemental Anal. Calcd. for C16H12BrNO3S: C
50.81 %; H 3.20 %, N 3.70 %. Found: C 50.79 %, H 3.22 %,
and N 3.72 %.
7e: Light yellow solid; Yield = 3.09 gms (90%); m.p. 212
ꢀC; IR (KBr) 1695 cm-1 (sharp, strong, –CO), and a strong
unequal doublet at 1170 and 1114 cm-1 (due to –SO2); H-
1
NMR (DMSO-d6/TMS): ꢁ 2.63 (s, 3H, -CH3), 7.19-8.19 (m,
8H, five phenyl an+ three aryl protons of the indole ring),
8.60 (s, 1H, ꢂ -proton of the indole ring); MS m/z: 345 (M+.
+1); Elemental Anal. Calcd. for C16H12N2O5S: C 55.81 %, H
3.51 %, N 8.14 %. Found: C 55.83 %, H 3.53 %, and N 8.16
%.
ACKNOWLEDGEMENTS
General Procedure for the Preparation of 8 from 7
The authors are highly indebted to the authorities of
Jawaharlal Nehru Technological University Hyderabad for
providing laboratory facilities. They are also thankful to the
A mixture of 7 (10 mmol) and NaBH4 (0.42 gms, 11
mmol) in methanol was stirred at room temperature for 3

An Unusual and Chemoselective Reduction of Ester Grouping
Letters in Organic Chemistry, 2012, Vol. 9, No. 3
197
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New Delhi, for providing financial support.
CONFLICT OF INTEREST
Declared none.
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